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Two purple-flowered plants can have white-flowered babies. How?
Genetic Inheritance lab · Last updated: 16 October 2026
Two purple-flowered plants can have white-flowered offspring. How? In this 3D lab, you cross plants, track the genes each parent passes on and predict the colours of the next generation. It explains why you can show traits neither parent shows, using the same patterns first spotted in garden peas.
What you'll discover
- Each parent passes on one copy of a gene, so every offspring carries two copies.
- A dominant version can hide a recessive one, so a purple plant can secretly carry the gene for white.
- When two such hidden carriers are crossed, on average about one offspring in four has white flowers.
The science in plain words
Living things inherit characteristics through genes, which come in different versions called alleles. Each plant or animal carries two copies of most genes, one from each parent. In the 1860s Gregor Mendel studied pea plants and noticed that some traits seemed to vanish in one generation and then reappear in the next.
In peas, the allele for purple flowers is dominant and the allele for white flowers is recessive. A plant with at least one purple allele has purple flowers. Only a plant with two white alleles has white flowers. So a purple plant can look purple yet carry a hidden white allele.
When two of these mixed purple plants are crossed, each parent passes on either its purple or its white allele, with equal chance. A Punnett square shows the four equally likely combinations: one with two purple alleles, two with one of each and one with two white alleles. On average three quarters of the offspring are purple and one quarter are white, a 3 to 1 ratio. With small numbers of seeds the real result can wander from this, just as tossing a coin four times does not always give two heads. The same rules apply to many single-gene traits in plants, animals and people.
Where it fits
- India, NCERT: Class 10 science, Chapter 8: Heredity
- United States: Grades 6 to 12
- Next Generation Science Standards: MS-LS3-2, HS-LS3-3
Common questions
What is the difference between dominant and recessive genes?
A dominant allele shows its effect even when only one copy is present. A recessive allele only shows when an organism has two copies of it. A recessive trait can therefore stay hidden for a generation and reappear when two carriers have offspring.
Can two brown-eyed parents have a blue-eyed child?
Yes, it can happen. Eye colour is controlled by several genes, but versions linked to blue eyes can be carried hidden by brown-eyed parents. If both pass those versions on, the child may have blue eyes. Real eye colour inheritance is more complex than one simple gene.
What is a Punnett square?
A Punnett square is a small grid used to predict the offspring of a cross. One parent's possible alleles go along the top and the other's down the side, and each box shows a possible combination. It shows the chances of each result, not exact numbers.
Related labs
- DNA Replication: Before a cell divides it copies all its DNA. How does it copy it so well?
- Natural Selection: Why do living things fit where they live so well? Watch hungry birds change a moth population.
- Probability: Each bounce is a coin toss. Why do a hundred balls always pile up into the same shape?
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Try it yourself
The Genetic Inheritance lab is one of the interactive 3D science labs inside Taz. Change one thing, predict what will happen, then run it and watch. Labs open after you sign in.